Nitride-based semiconductor materials having high electric field strength are highly expected to be applied to semiconductor devices for power electronics, high frequency power semiconductors, or the like. However, it is also known that they suffer from a phenomenon called current collapse in which a drain current decreases significantly during application of a stress such as a high voltage, which influences the characteristics of semiconductor devices. Moreover, reduction in a gate leakage current indeed needs to be achieved to increase a breakdown voltage of a semiconductor device, and use of a gate insulation film is known to be useful in achieving the purpose.
In order to realize a high performance nitride-based semiconductor device, it is demanded to achieve a configuration which can take balance between suppression of the current collapse and reduction in the gate leakage current.